The object of the present invention is a method for surface optical inspection of long products in production or working plants, also at high temperature.
By an exemplary way the inspected product can be a bloom, a slab, a billet, a bar, a wire rod, a wire, a sheet, a tape, or a beam, obtained by rolling, drawing, grinding and other methods commonly used in continuous or batch production, consisting of any material like steel, metallic alloys, plastic, ceramics, wood, paper or other.
As it is known, the presence or absence of surface defects is a major criterion in order to estimate the quality of long products and in order to prevent the refusal or replacement demand of defective products by purchasers.
Therefore various systems in order to resolve the problem of surface inspection of long products and detection of related surface defects have been suggested. Some used systems are described in U.S. Pat. No. 6,859,285 B1, US 2002/0008203 A1 and EP 1 582 068 B1.
In U.S. Pat. No. 6,950,546 B2, said problem, for example, has been resolved using a system comprising: a plurality of illuminators disposed around the long product, each one projecting light with a set angle with respect to line perpendicular to lightened surface; a plurality of image detectors, disposed around the long product, having main axis inclined with respect to said line with a second set angle; and a computerized unit for acquisition and processing of said images.
The sensitivity of these systems and ability thereof to measure both small and wide angles of occurring discontinuities are not however completely satisfactory.
In FR2873207A1 a device the use thereof seems to involve a method in order to inspect the surface and detect defects of long products during working consisting of the following steps is described:
illuminating an annular portion of surface of the long product with a plurality of illuminators each one projecting light with a set angle with respect to line perpendicular to lightened surface;
detecting reflexed images by a plurality of detectors having main axis inclined with respect to said line with a second set angle;
acquiring and processing said images by means of a computerized unit; and
using a combination of images of the same region of the long product, said images being taken under different lighting conditions, in order to rebuilt shape of surface and thus obtaining information about the presence of defects.
However in the specific field the need to have of a system resulting in improved detection sensitivity and flexibility exists.